Arrange the following steps of gel electrophoresis in correct order.
A. DNA fragments were forced to move towards anode under electric field through agarose gel
B. Staining DNA fragments with Ethidium Bromide.
C. DNA fragments separated according to their size.
D. Visualising them in UV rays
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A, C, B, D
DNA fragments move towards the anode through the agarose gel (A) and separate by size (C); the gel is then stained with ethidium bromide (B) and seen under UV light (D).
NCERT Extract:
Restriction Enzymes – “… Since DNA fragments are negatively charged molecules they can be separated by forcing them to move towards the anode under an electric field through a medium/matrix. Nowadays the most commonly used matrix is agarose which is a natural polymer extracted from sea weeds. The DNA fragments separate (resolve) according to their size through sieving effect provided by the agarose gel. Hence, the smaller the fragment size, the farther it moves.”
Restriction Enzymes – “The separated DNA fragments can be visualised only after staining the DNA with a compound known as ethidium bromide followed by exposure to UV radiation (you cannot see pure DNA fragments in the visible light and without staining). You can see bright orange coloured bands of DNA in a ethidium bromide stained gel exposed to UV light (Figure 9.3). The separated bands of DNA are cut out from the agarose gel and extracted from the gel piece. This step is known as elution.”